The human immunodeficiency virus type 1 (HIV-1) Tat protein is a key regulatory protein in the HIV-1 replication cycle. Wild-type Tat gene of HIV-1 is required for production of viral RNA and viral replication. Tat interacts with cellular transcriptional factors and cytokines, such as tumor necrosis factor-alpha (TNF-alpha), and alters the expression of a variety of genes in HIV-1-infected and non-infected cells. Tat function requires its binding to a cellular positive transcription elongation factor b (P-TEFb).
The presence of Tat specific cytotoxic T lymphocytes is correlated with strong resistance to HIV infection (Allen et al. Nature 2000 407(6802):386–390). Tat mediated pathogenic effects can also be neutralized by anti-Tat antibodies. Antibodies directed against conserved regions of Tat, such as the cysteine rich and the lysine rich domains, have been shown to be particularly effective in inhibiting HIV replication. In HIV-1-infected patients, a strong humoral immune response against HIV-1 Tat protein is inversely correlated to peripheral blood viral load (Re et al. J. Clin. Virol. 2001 21(1):81–9)
Wild-type Tat also promotes lymphocyte infiltration and adhesion primarily by its binding to VEGF receptor and its subsequent dimerization and activation (Mitola et al. Blood 1997 90(4):1365–72). This effort is primarily mediated by the basic domain of Tat.
Wild-type Tat modified to be defective in binding to TAR has been shown to be effective in inhibiting viral long terminal repeat (LTR) transactivation (Modesti et al. New Biol. 1991 3(8):759–68).
Tat has also been shown to be taken up and internalized by cells. Thus, fusion of a heterologous protein to Tat has been proposed as a means for cellular delivery of heterologous proteins in cell culture and living animals.
However, Tat has also been linked with multiple pathogenic effects. For example, numerous studies indicate a role for the HIV regulatory protein Tat in HIV-related inflammatory and neurodegenerative processes. HIV-1 Tat protein has been linked to dementia associated with HIV infection. In addition, the Tat protein has been directly implicated in the pathogenesis of AIDS-related Kaposi's sarcoma. More recently, with the advent of agents which prolong the life of HIV-infected patients, secretion of the Tat protein has been implicated in multiple cardiovascular diseases observed in these patients (Krishnaswamy et al. Cardiology in Review 2000 8(5):260–8). Thus, while Tat administration has multiple utilities, it also causes multiple pathogenic effects.
In the present invention, variants of Tat, referred to herein as Super-Tats, are provided which exhibit similar but enhanced activities as compared to wild-type Tat. Accordingly Super-Tats of the present invention can be administered at lower levels in clinical application thereby minimizing pathogenic effects associated with Tat administration.